1. Field of the Invention
The present invention relates generally to wire bonding apparatus and method and, more particularly, to a wire bonding apparatus capable of self-recovery when a wire disconnection occurs and a method for automatically forming a ball.
2. Description of the Related Art
Various methods may be implemented to electrically connect together a semiconductor chip to other components in a semiconductor package assembly. For example, wire bonding, flip chip bonding and tape automated bonding (TAB) methods may be employed to achieve such connections.
Among these methods, the wire bonding method using Au wire (for example) may be well known and employed in semiconductor package manufacture techniques. Au wire may have a lower bonding strength than other wire materials (such as Al or Cu wire, for example). Notwithstanding, the use of Au wire may have associated advantages. For example, Au wire may be more oxidation and contamination resistant as compared to other wire materials. Also, Au wire may be elongated and formed into a substantially spherical ball more easily as compared to other wire materials.
FIG. 1 illustrates a structure of a conventional wire bonding apparatus 50. Here, a wire 41 may be provided from a wire spool 39 and inserted into a capillary 32 through a wire clamp 33. The capillary 32 may include a transducer 31. The transducer 31 may transmit to the capillary 32 energy generated from an ultrasonic generator (not shown). The wire clamp 33 may be installed over the capillary 32 and configured to clamp the wire 41. A wire bonding monitoring system (WBMS) 38 may monitor the position and arrangement of a wiring substrate 20 and a semiconductor chip 24 before a wire bonding process occurs. The WBMS 38 also may transmit current to the transducer 31 during the wire bonding and monitor the current. When the wire 41 is disconnected during the wire bonding, the WBMS 38 may detect the change of the current value and transmit wire disconnection information to a host computer 37.
The wire clamp 33 may be controlled by the host computer 37. The wire clamp 33 may have a pair of plates between which the wire 41 may be clamped. The host computer 37 may manage a plurality of wire bonding apparatuses 50. The host computer 37 may transmit to a driver 34 a profile for controlling the opening and/or closing of the wire clamp 33 through a communication board 35, such as a digital to analog converter (DAC), for example. The profile from the host computer 37 may be considered as a control signal having plurality of time segments. During each time segment, the driver 34 may open or close the wire clamp 33. As the time segments become shorter, the profile may become finer. However, due to (among other things) the characteristics of the host computer 37, it may be difficult to reduce the length of a time segment to 500 μS or less. In other words, it may be difficult to change the state of the wire clamp 33 (from an opened condition to a closed condition, and vice versa) in 500 μs or less using the host computer 37.
A conventional wire bonding process using the wire bonding apparatus 50 is described below. The wire 41 may pass from the wire spool 39 through the transducer 31 and the capillary 32, while maintaining a predetermined tension by an air tension unit 40. The air tension unit 40 may maintain the predetermined tension by blowing air 42 across the wire 41. A high voltage spark blade (not shown) may apply an electric frame off (EFO) fire to a tail of the wire 41 to form a ball. A ball bonding process may be performed on an electrode pad 26 of the semiconductor chip 24. A loop having a predetermined trace may be formed. A stitch bonding process may be performed on a substrate pad of the wiring substrate 20. During the ball bonding and the stitch bonding processes, ultrasonic energy may be applied to the capillary 32 through the transducer 31 and heat may be applied to a target bonding area.
Faults may occur in the wire 41 during the wire bonding process. For example, the wire 41 may be inadvertently disconnected (e.g., experience a break) due to excessive force or material bouncing (for example), which may be applied to the capillary 32 during the stitch bonding process. When faults occur, the wire bonding apparatus 50 may stop operating. The operator may manually reinsert an end of the wire 41 into the capillary 32. The reinsertion operation may take a significant amount of time depending on (among other things) the skill of the operator. Such manual intervention by the operator may result in a reduction of productivity.
In an effort to overcome the drawbacks noted above, a wire bonding apparatus having a “self-recovery” feature has been conventionally implemented. When an inadvertent wire disconnect occurs, the “self-recovery” apparatus may automatically form a wire tail and then a ball, thereby allowing the wire bonding process to continue without operator intervention. Although conventional “self-recovery” apparatuses are generally thought to provide acceptable performance, they are not without shortcomings. For example, because the host computer 37 controls the opening and closing of the wire clamp of the wire bonding apparatus, a clamping operation of the wire clamp 33 may be ineffective when an inadvertent wire disconnect occurs. Specifically, if the wire becomes disconnected during the wire bonding process, the WBMS 38 may detect the change of the current flowing at the transducer 31 and transmit corresponding information to the host computer 37. The WBMS 38 may then receive signals from the host computer 37 to clamp the wire 41. It may take 1,000 μs or more from the occurrence of the inadvertent wire disconnect to the clamping operation. During this time, the wire 41 may slip and may become altogether removed from the capillary 32. Accordingly, notwithstanding the “self-recovery” feature, the operator may need to manually reinsert the end of the wire 41 into the capillary 32.
Further, the tail of the disconnected wire may be deformed in comparison with that of a normal wire. The use of the disconnected wire may result in abnormal ball formation, thereby resulting in a wire bonding fault.